As a part of a comprehensive investigation of the reversible aggregation (or micelle formation) of bile salts in solutions, this project deals with the kinetic relaxation studies in the dynamic range from a microsecond to a second. A combined stopped-flow temperature-jump apparatus, already available with spectrophotometric detection, is being rebuilt for fluorescence and light scattering detection. In order to render bile salts chromophoric, suitable compounds (for example, aromatic amino acids, naphthalene derivatives) are coupled through peptide linkage to the carboxyl group of the side chain of bile salts leaving the steroid part intact. Oxamic acid, H2NCOCO2H, is particularly attractive candidate for this purpose. The size and hydrophobibity are similar to those of glycine and taurine. (The oxamic derivatives of bile salts absorb strongly in UV region. High pressure liquid chromatographic procedures for separation and purification of bile salts and their chromophoric derivatives are developed on a preparative scale. The apparent volume of bile salts is being systematically investigated from high-precision density measurements.